Authors

Files

Faculty Sponsor

Dr. Robert Gillespie

Department/Program

Department of Biology

University Affiliation

Indiana University – Purdue University Fort Wayne

Abstract

Agriculture is the most extensive land use activity in Ohio and Indiana. This has led to an influx of agricultural chemicals to receiving headwater streams. Atrazine, one of the most commonly detected herbicides in agriculturally-dominated watersheds, has been shown to cause feminization of male gonads in frogs and zebrafish in laboratory exposures. Vitellogenin (Vtg), produced in the liver, is an egg yolk precursor that is deposited in the ovaries of fish and amphibians. Since Vtg is induced by estrogen and estrogen-like chemicals it is a useful biological marker for feminization of male frogs and fish. Because of the documented feminization of male frogs by atrazine, we hypothesized that exposure of fishes to agricultural drainage water would cause induction of Vtg in male fish. To test this hypothesis, we measured concentrations of Vtg in livers of male fishes that inhabit agricultural ditches (field sites) and fishes that were experimentally-exposed to ditch water (bioassays) from drainage ditches. We used an ELISA technique to quantify Vtg in livers of male creek chubs from field sites and livers of male fathead minnows from bioassays. Differences in concentrations of Vtg among treatments were analyzed for statistical significance by t-test (P<0.05). We hypothesized that livers from male fishes exposed to agricultural drainage water would have significantly greater Vtg than those from fish in reference treatments. However, the data did not support our hypothesis. We found no significant differences in Vtg concentrations between fish from ditch and reference sites. The apparent lack of effect of agrichemicals on Vtg in chubs and fatheads may have resulted from 1) a lack of sensitivity to agrichemicals, 2) concentrations of chemicals that were below the threshold that causes endocrine disruption, 3) lack of estrogenic activity of chemical exposure. Concentrations of atrazine in ditches rarely exceeded 8 ug/L which is well below that known to cause chronic toxicity (65 ug/L) in fishes. Results from published research suggests that atrazine in ditch water did not cause induction of Vtg in fathead minnows, but may have caused increased concentration of Vtg in trout exposed to atrazine in the laboratory. Future studies should use more sensitive species, such as bluegill and bass, and include assessments of the impacts of agrichemicals on reproductive output in fishes.